Impact will occur between 05:49 and 5:55 UT July 4th or 5:52 +/- 3 minutes. We selected this time to be sure three conditions were covered. First we need to have two Deep Space Network (DSN) stations able to receive data from the spacecraft. Secondly, we wanted a good ground-based observing site in darkness to observe the comet, and third, we want the Hubble Space Telescope in a position to observe the impact. We have been monitoring the predicted times of Hubble orbits to set the time and coordinate with engineers who execute trajectory correction maneuvers.

Comet Tempel 1 will be near Spica (alpha Vir), the bright star in the constellation Virgo. You can find more detailed star charts on our amateur website, or use your favorite planetarium program to generate charts for your specific location.

The comet overtakes the impactor at a closing velocity of 10 km/s or 23,000 mph. At that time, the impactor disintegrates upon impact and a shock wave carrying the energy of the moving s/c mass plows into the comet. Depending on structure of the comet (density and porosity) the shock wave will travel a short distance or a long distance. If the comet is sticky and strong, then the energy is stopped by the comet, and the wave rebounds, carrying material with it into a rising plume of gas and dust. Learn more about how craters form on our Cratering page.

The comet will be about magnitude 9 before impact. You should be able to see that in a modest telescope. We anticipate releasing enough gas and dust into the coma of the comet to brighten it to about magnitude 6. This is a bit brighter and from dark locations you might be able to see a dim fuzzball in binoculars. How fast the comet will brighten, how long it will be 'bright' and exactly how bright it will get is unknown. That is why we hope amateurs all over the world watch the comet and take measurements so we can find out this information.

This is the side of Earth that will "see" the comet at impact. Unfortunately, even though the comet is above the horizon for observers in Australia, it is still daylight and they will have to wait for dark. Look to the upper right and you can just make out the West Coast of the United States. Of course, we won't know what the cloud cover will be like that day. This is just a simulation from the Solar System Simulator.

Before impact, you will see a very dim fuzzball through a telescope. After impact, we expect that you will see a brighter fuzzball through the telescope. How much brighter is just a guess, but our best one right now is that we will make the comet about 3 magnitudes brighter (from magnitude 9 to about magnitude 6). The impact may also create jets, but those may only be visible in larger telescopes or with image processing.

NASA TV programming will be showing the images from the flyby and impactor (before it hits). You can learn how to access NASA TV via satellite and the web at www.nasa.gov/multimedia/nasatv/. Some observatories may also be broadcasting images of the comet before and after impact. Stay tuned as we learn which ones will be available. At this time, there is one robotic telescope (SLOOH.com) that delivers live color images to the internet from telescopes in the Canary Islands to which you can subscribe. They'll see the comet about 14 hours after impact. The East Coast of the US will see the comet about 19 hours after impact (right during 4th of July fireworks!).

Using PI scaling, the estimated angle of approach (25 degrees from the horizontal), a mass of 370 kg, velocity of impact 10.2 km/sec and a sand target (similar to that for Tempel 1), a crater of about 10 m in size would be formed if the impact were to have occurred on the Earth. So why would the size of the crater differ on the comet than one formed under similar conditions on Earth? Not everything is the same! The Earth is far more massive and has an atmosphere. Read through Cratering for more information.

You can also take a look at Dr. Melosh's 'Crater' Routine and calculate the size of craters using different projectile descriptors, impact conditions, and target descriptions.